Lithium-ion battery and apparatus

ABSTRACT

This application provides a lithium-ion battery and an apparatus. The lithium-ion battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. A positive active material of the positive electrode plate includes Li x1 Co y1 M 1-y1 O 2-z1 Q z1 , where 0.5≤x1≤1.2, 0.8≤y1≤1.0, 0≤z1≤0.1, M is selected from one or more of Al, Ti, Zr, Y, and Mg, and Q is selected from one or more of F, Cl, and S. The electrolyte contains an additive A that is a polynitrile six-membered nitrogen-heterocyclic compound with a relatively low oxidation potential. The lithium-ion battery has superb cycle performance and storage performance, especially under high-temperature and high-voltage conditions.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent application Ser. No. 17/056,805, filed on Dec. 13, 2019, which is a National Stage of International Application No. PCT/CN2019/125310, filed on Dec. 13, 2019. The International Application claims priority to Chinese Patent Application No. 201811535449.2, filed on Dec. 14, 2018. The aforementioned patent applications are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

This application relates to the field of energy storage materials, and in particular, to a lithium-ion battery and an apparatus.

BACKGROUND

Lithium-ion batteries are widely applied to electromobiles and consumer electronic products due to their advantages such as high energy density, high output power, long cycle life, and low environmental pollution. Current requirements on lithium-ion batteries are high voltage, high power, long cycle life, long storage life, and superb safety performance.

Currently, LiCoO₂ is widely used as a positive active material in lithium-ion batteries and shows relatively stable performance during cycling between fully discharged LiCoO₂ and semi-charged Li_(0.5)CoO₂ (4.2 V vs. Li). Therefore, lithium ions that are actually used account only for ½ of lithium ions actually contained in LiCoO₂. When the voltage is greater than 4.2 V, the remaining ½ of lithium ions contained in LiCoO₂ may continue to be extracted. However, during deep delithiation, Co³⁺ is oxidized into quite unstable Co⁴⁺, which oxidizes an electrolyte together with surface oxygen that loses a large quantity of electrons. In this case, a large amount of gas is produced inside the batteries, causing the batteries to swell. In addition, due to a corrosive effect of HF in the electrolyte on a surface of a positive electrode, Co⁴⁺ is dissolved in the electrolyte and deposited on a surface of a negative electrode, catalyzing reduction of the electrolyte, and also producing a large amount of gas that causes the batteries to swell. In addition, due to high overlapping between a 3d energy level of Co and a 2p energy level of O, the deep delithiation also causes lattice oxygen to lose a large quantity of electrons, resulting in sharp shrinkage of LiCoO₂ unit cells along a c-axis direction, and leading to instability or even collapse of a local bulk structure. This eventually causes loss of LiCoO₂ active sites, and a rapid decrease in capacity of the lithium-ion batteries. Therefore, LiCoO₂ has very poor performance when being used in a high-voltage system greater than 4.2 V.

In view of this, this application is hereby proposed.

SUMMARY

In view of the problems in the background, an objective of this application is to provide a lithium-ion battery and an apparatus. The lithium-ion battery has superb cycle performance and storage performance, especially under high-temperature and high-voltage conditions.

To achieve the foregoing objective, according to a first aspect, this application provides a lithium-ion battery, including an electrode assembly and an electrolyte, wherein the electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. A positive active material of the positive electrode plate includes Li_(x1)Co_(y1)M_(1-y1)O_(2-z1)Q_(z1), where 0.5≤x1≤1.2, 0.8≤y1≤1.0, 0≤z1≤0.1, M is selected from one or more of Al, Ti, Zr, Y, and Mg, and Q is selected from one or more of F, Cl, and S. The electrolyte contains an additive A that is selected from one or more of compounds represented by Formula I-1, Formula 1-2, and Formula 1-3. In the Formula I-1, the Formula I-2, and the Formula I-3, R₁, R₂, R₃, and R₄ each are independently selected from a hydrogen atom, a halogen atom, a substituted or unsubstituted C₁-C₁₂ alkyl group, a substituted or unsubstituted C₁-C₁₂ alkoxy group, a substituted or unsubstituted C₁-C₁₂ amine group, a substituted or unsubstituted C₂-C₁₂ alkenyl group, a substituted or unsubstituted C₂-C₁₂ alkynyl group, a substituted or unsubstituted C₆-C₂₆ aryl group, or a substituted or unsubstituted C₂-C₁₂ heterocyclic group, where a substituent group is selected from one or more of a halogen atom, a nitrile group, a C₁-C6 alkyl group, a C₂-C₆ alkenyl group, and a C₁-C₆ alkoxy group; x, y, and z each are independently selected from integers 0-8; and m, n, and k each are independently selected from integers 0-2.

According to a second aspect of this application, this application provides an apparatus, including the lithium-ion battery as described in the first aspect of this application.

Compared with the prior art, this application provides at least the following beneficial effects: In this application, a positive active material that contains a metal ion M-doped lithium cobalt oxide material Li_(x1)Co_(y1)M_(1-y1)O_(2-z1)Q_(z1) is used, where the doping element M serves as a framework in the lithium cobalt oxide material. This could reduce lattice deformation of the lithium cobalt oxide material during deep delithiation, delay degradation of bulk structure of the lithium cobalt oxide material, and improve structural stability of the lithium-ion battery when the lithium-ion battery is used at a high voltage greater than 4.2 V. The electrolyte used in this application also contains a polynitrile six-membered nitrogen-heterocyclic compound with a relatively low oxidation potential, such that a stable complex layer can be formed on a surface of the positive active material during formation of the battery. This could effectively passivate the surface of the positive active material, reduce surface activity of the positive active material, and suppress dissolution of a transition metal (especially cobalt) into the electrolyte, thereby reducing gas production of the battery while reducing side reactions. Therefore, the lithium-ion battery of this application has superb cycle performance and storage performance, especially under high-temperature and high-voltage conditions. The apparatus of this application includes the lithium-ion battery as described in the first aspect of this application, and therefore provides at least the same advantages as the lithium-ion battery.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows carbon nuclear magnetic resonance spectroscopy of a compound A1.

FIG. 2 shows carbon nuclear magnetic resonance spectroscopy of a compound A2.

FIG. 3 shows carbon nuclear magnetic resonance spectroscopy of a compound A3.

FIG. 4 is a schematic diagram of an embodiment of a lithium-ion battery.

FIG. 5 is a schematic diagram of an embodiment of a battery module.

FIG. 6 is a schematic diagram of an embodiment of a battery pack;

FIG. 7 is an exploded diagram of FIG. 6.

FIG. 8 is a schematic diagram of an embodiment of an apparatus using a lithium-ion battery as a power source.

Reference numerals in the accompanying drawings are described as follows:

-   -   1. battery pack;         -   2. upper cabinet body;         -   3. lower cabinet body;         -   4. battery module; and             -   5. lithium-ion battery.

DESCRIPTION OF EMBODIMENTS

The following describes in detail the lithium-ion battery and apparatus according to this application.

A lithium-ion battery according to a first aspect of this application is described first.

The lithium-ion battery according to this application includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator.

A positive active material of the positive electrode plate includes Li_(x1)Co_(y1)M_(1-y1)O_(2-z1)Q_(z1), where 0.5≤x1≤1.2, 0.8≤y1≤1.0, 0≤z1≤0.1, M is selected from one or more of Al, Ti, Zr, Y, and Mg, and Q is selected from one or more of F, Cl, and S. The electrolyte contains an additive A that is selected from one or more of compounds represented by Formula I-1, Formula I-2, and Formula I-3.

In the Formula I-1, the Formula I-2, and the Formula I-3, R₁, R₂, R₃, and R₄ each are independently selected from a hydrogen atom, a halogen atom, a substituted or unsubstituted C₁-C₁₂ alkyl group, a substituted or unsubstituted C₁-C₁₂ alkoxy group, a substituted or unsubstituted C₁-C₁₂ amine group, a substituted or unsubstituted C₂-C₁₂ alkenyl group, a substituted or unsubstituted C₂-C₁₂ alkynyl group, a substituted or unsubstituted C₆-C₂₆ aryl group, or a substituted or unsubstituted C₂-C₁₂ heterocyclic group, where a substituent group (indicating a substitution case in the “substituted or unsubstituted” mentioned in this application) is selected from one or more of a halogen atom, a nitrile group, a C₁-C₆ alkyl group, a C₂-C₆ alkenyl group, and a C₁-C₆ alkoxy group; x, y, and z each are independently selected from integers 0-8; and m, n, and k each are independently selected from integers 0-2.

The lithium-ion battery of this application has superb cycle performance and storage performance, especially under high-temperature and high-voltage conditions.

Details are as follows:

(1) In this application, a positive active material that contains a metal ion M-doped lithium cobalt oxide material Li_(x1)Co_(y1)M_(1-y1)O_(2-z1)Q_(z1) is used, where the doping element M serves as a framework in the lithium cobalt oxide material. This could reduce lattice deformation of the lithium cobalt oxide material during deep delithiation, delay degradation of bulk structure of the lithium cobalt oxide material, and improve structural stability of the lithium-ion battery when the lithium-ion battery is used at a high voltage greater than 4.2 V.

(2) The additive A contained in the electrolyte in this application is a polynitrile six-membered nitrogen-heterocyclic compound with a relatively low oxidation potential. Nitrogen atoms in the nitrile groups contain lone pair electrons, which have relatively strong complexation with a transition metal in the positive active material. After being applied in the electrolyte, the additive A may be adsorbed on a surface of the positive active material during formation of the battery to form a loose and porous complex layer and effectively passivate the surface of the positive active material. The complex layer could avoid direct contact between the surface of the positive active material and the electrolyte and reduce surface activity of the positive active material, and could further reduce a large quantity of side reactions on the surface of the positive active material and suppress dissolution of a transition metal (especially cobalt) into the electrolyte. Therefore, the electrolyte in this application may have an effect of reducing side reaction products and reducing gas production.

(3) The additive A in this application has a special six-membered nitrogen-heterocyclic structure. A spacing between nitrile groups is closer to that between transition metals on the surface of the positive active material. This could maximize complexation of the nitrile groups and allow more nitrile groups to have a complexation effect. Therefore, compared with a conventional linear nitrile compound, the polynitrile six-membered nitrogen-heterocyclic compound in this application has a better passivation effect.

(4) The special six-membered nitrogen-heterocyclic structure of the additive A in this application can further lower an oxidation potential of molecules, so that a stable complex layer may be formed on the surface of the positive active material during formation of the battery. This may help improve electrochemical performance of an entire battery system, for example, by reducing gas production and extending a cycle life under high-temperature and high-voltage conditions.

In the lithium-ion battery of this application, preferably, based on total mass of the electrolyte, mass percent of the additive A is 0.1%-10%. If the amount of the additive A is too low, improvement made by the additive A to the electrolyte is not obvious; if the amount of the additive A is too high, the complex layer formed by the additive A being adsorbed on the surface of the positive active material would be too thick and dense, affecting diffusion and migration of lithium ions, and greatly increasing positive electrode impedance. In addition, excessively high amount of the additive A further causes an increase in overall viscosity of the electrolyte and a decrease in an ionic conductivity, and therefore, affects performance of the lithium-ion battery. Preferably, an upper limit of the amount of the additive A may be any one selected from 10%, 9%, 8%, 7%, 6%, 5%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, 1%, or 0.8%, and a lower limit of the amount of the additive A may be any one selected from 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or 1.2%.

More preferably, based on the total mass of the electrolyte, the mass percent of the additive A is 0.1%-6%. Even more preferably, based on the total mass of the electrolyte, the mass percent of the additive A is 0.1%-3.5%.

In an embodiment of the lithium-ion battery of this application, the electrolyte may further contain an additive B that is LiBF₄. In a high-voltage lithium-ion battery system, a positive active material easily releases oxygen, and atoms B in LiBF₄ can stabilize oxygen atoms in the positive active material and have an effect of suppressing oxygen release of the positive active material, thus contributing to extension of a life, especially a storage life, of the high-voltage lithium-ion battery system.

Preferably, based on total mass of the electrolyte, mass percent of the additive B is 0.1%-10%. More preferably, based on the total mass of the electrolyte, the mass percent of the additive B is 0.1%-5%.

In another embodiment of the lithium-ion battery of this application, the electrolyte may further contain an additive C that is selected from one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), and 1,3-propane sultone (PS). The additive C may further form, on surfaces of positive and negative electrodes, a surface film containing one or more of double bonds, fluorine atoms, and sulfonate groups. The surface film has good chemical, electrochemical, mechanical, and thermal stability, and can avoid direct contact between the electrolyte and the surfaces of the positive and negative electrodes while smoothly conducting lithium ions, thereby providing an effect of suppressing oxidation and reduction side reactions on the surfaces of the positive and negative electrodes. Therefore, this may significantly suppress gas production of the battery, and improve a cycle life and a storage life of a high-voltage lithium-ion battery system.

Preferably, based on total mass of the electrolyte, mass percent of the additive C is 0.1%-10%. More preferably, based on the total mass of the electrolyte, the mass percent of the additive C is 0.1%-5%.

In still another embodiment of the lithium-ion battery of this application, the electrolyte may further contain both an additive B and an additive C. Preferably, based on total mass of the electrolyte, mass percents of the additive B and the additive C are independently 0.1%-10%.

In the lithium-ion battery of this application, the electrolyte further includes an organic solvent and a lithium salt.

The organic solvent used in the electrolyte in an embodiment of this application may include a cyclic carbonate and a chain carbonate, and could further improve cycle performance and storage performance of the lithium-ion battery under high-temperature and high-voltage conditions. In addition, it is easy to adjust a conductivity of the electrolyte to a suitable range, thus further helping the additives achieve a better film-forming effect.

The organic solvent used in the electrolyte in an embodiment of this application may further include a carboxylic acid ester. To be specific, the organic solvent in this application may include a mixture of a cyclic carbonate, a chain carbonate, and a carboxylic acid ester. The carboxylic acid ester is characterized by large dielectric constant and low viscosity, and could effectively prevent association of lithium ions and anions in the electrolyte. In addition, the carboxylic acid ester is more advantageous than the cyclic carbonate and the chain carbonate in terms of ion conduction. Especially at low temperature, the carboxylic acid ester could ensure good ion conduction for the electrolyte.

Based on total mass of the organic solvent, mass percent of the cyclic carbonate may be 15%-55%, preferably 25%-50%; mass percent of the chain carbonate may be 15%-74%, preferably, 25%-70%; and mass percent of the carboxylic acid ester may be 0.1%-70%, preferably, 5%-50%.

Specifically, the cyclic carbonate may be selected from one or more of an ethylene carbonate, a propylene carbonate, a 1,2-butylene carbonate, and a 2,3-butanediol carbonate. More preferably, the cyclic carbonate may be selected from one or more of an ethylene carbonate and a propylene carbonate.

Specifically, the chain carbonate may be one or more asymmetric chain carbonates selected from an ethyl methyl carbonate, a methyl propyl carbonate, a methyl isopropyl carbonate, a methyl butyl carbonate, and an ethyl propyl carbonate; the chain carbonate may also be one or more symmetric chain carbonates selected from a dimethyl carbonate, a diethyl carbonate, a dipropyl carbonate, and a dibutyl carbonate; the chain carbonate may also be a mixture of the asymmetric chain carbonate and the symmetric chain carbonate.

Specifically, the carboxylic acid ester may be selected from one or more of methyl pivalate, ethyl pivalate, propyl pivalate, butyl pivalate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl acetate, ethyl acetate, propyl acetate, and butyl acetate.

The lithium salt used in the electrolyte in an embodiment of this application may be selected from one or more of LiPF₆, LiPO₂F₂, Li₂PO₃F, LiSO₃F, lithium trifluoro((methanesulfonyl)oxy)borate, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, lithium bis[oxalate-O,O′] borate, difluorobis[oxalate-O,O′] lithium phosphate, and tetrafluoro[oxalate-O,O′] lithium phosphate.

In the lithium-on battery of this application, concentration of the lithium salt is not particularly limited, and may be adjusted according to actual needs.

In the lithium-ion battery of this application, preferably, the conductivity at 25° C. of the electrolyte is 4 mS/cm-12 mS/cm.

In the lithium-ion battery of this application, a preparation method for the electrolyte is not limited, and the electrolyte may be prepared according to a method for a conventional electrolyte.

In the lithium-ion battery of this application, Li_(x1)Co_(y1)M_(1-y1)O_(2-z1)Q_(z1) may be specifically selected from one or more of LiCo_(0.9)Zr_(0.1)O₂, LiCo_(0.9)Ti_(0.1)O₂, Li_(1.05)Co_(0.8)Mg_(0.2)O₂, Li_(1.01)Co_(0.98)Mg_(0.01)Ti_(0.005)Al_(0.0005)O₂, Li_(1.05)Co_(0.98)Mg_(0.005)Zr_(0.005)T_(0.01)O_(1.9)F_(0.1), Li_(1.1)Co0.95Mg_(0.01)Zr_(0.01)Al_(0.03)O₂, Li_(1.04)Co_(0.95)Mg_(0.02)Zr_(0.03)O_(1.95)F_(0.05), Li_(1.06)Co_(0.96)Mg_(0.02)Ti_(0.02)O₂, Li_(1.08)Co_(0.97)Mg_(0.01)Zr_(0.01)Al_(0.01)O_(1.9)S_(0.1), Li_(1.09)Co_(0.98)Mg_(0.01)Ti_(0.0005)Al_(0.0005)O₂, Li_(1.085)Co_(0.98)Zr_(0.01)Ti_(0.005)Al_(0.005)O_(1.9)Cl_(0.1), Li_(1.03)Co_(0.96)Mg_(0.01)Zr_(0.01)Ti_(0.01)Al_(0.01)O₂, Li_(1.04)Co_(0.97)Zr_(0.01)Al_(0.02)O_(1.9)F_(0.1), Li_(1.07)Co0.97Zr_(0.01)Ti_(0.01)Al_(0.01)O_(1.9)S_(0.1), Li_(1.02)Co_(0.96)Mg_(0.02)Zr_(0.015)Ti_(0.005)O_(1.9)S_(0.1), Li_(1.03)Co_(0.98)Ti_(0.01)Al_(0.01)O_(1.9)Cl_(0.1), Li_(1.05)Co_(0.97)Mg_(0.01)Zr_(0.01)Al_(0.01)O_(1.9)Cl_(0.1), Li_(1.04)Co_(0.95)Zr_(0.02)Ti_(0.03)O_(1.9)F_(0.1), Li_(1.09)Co_(0.97)Mg_(0.02)Ti_(0.01)O_(1.95)F_(0.05), Li_(1.03)Co_(0.95)Mg_(0.03)Ti_(0.02)O_(1.9)S_(0.1), and Li_(1.04)Co_(0.97)Zr_(0.01)Ti_(0.01)Al_(0.01)O_(1.9)S_(0.1).

In the lithium-ion battery of this application, the positive active material may further include one or more of a lithium nickel oxide, a lithium manganese oxide, a lithium nickel manganese oxide, a lithium nickel cobalt manganese oxide, a lithium nickel cobalt aluminum oxide, and a compound obtained by adding another transition metal or non-transition metal to any of the foregoing oxide.

In the lithium-ion battery of this application, a negative active material in the negative electrode plate may be soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide compound, silicon carbon composite, lithium titanate, a metal that can form an alloy with lithium, or the like. One type of these negative active materials may be used alone, or two or more types may be used in combination.

In the lithium-ion battery of this application, the positive electrode plate further includes a binder and a conductive agent. A positive slurry including the positive active material, the binder, and the conductive agent is applied onto a positive current collector, and then dried to give the positive electrode plate. Types and amounts of the conductive agent and the binder are not specifically limited, and may be selected according to actual needs. A type of the positive current collector is not specifically limited either, and may be selected according to actual needs. Preferably, the positive current collector may be an aluminum foil.

Likewise, the negative electrode plate further includes a binder and a conductive agent. A negative slurry containing the negative active material, the binder, and the conductive agent is applied onto a negative current collector, and then dried to give the negative electrode plate. Types and amounts of the conductive agent and the binder are not specifically limited, and may be selected according to actual needs. A type of the negative current collector is not specifically limited either, and may be selected according to actual needs. Preferably, the positive current collector may be a copper foil.

In the lithium-ion battery of this application, the separator is disposed between the positive electrode plate and the negative electrode plate to have an effect of separation. A type of the separator is not specifically limited, and the separator may be, but not limited to, any separator materials used in existing lithium-ion batteries, for example, polyethylene, polypropylene, polyvinylidene fluoride, and a multilayer composite film thereof.

In the lithium-ion battery of this application, an end-of-charge voltage of the lithium-ion battery is not less than 4.2 V, that is, the lithium-ion battery may be used at a high voltage of not less than 4.2 V. Preferably, the end-of-charge voltage of the lithium-ion battery is not less than 4.35 V.

The lithium-ion battery of this application may be either a hard-shell lithium-ion battery or a soft-package lithium-ion battery. Preferably, a metal hard shell is used for the hard-shell lithium-ion battery. Preferably, a packaging bag is used as a battery housing of the soft-package lithium-ion battery. The packaging bag typically includes an accommodating portion and a sealing portion. The accommodating portion is configured to accommodate the electrode assembly and the electrolyte, and the sealing portion is configured to seal the electrode assembly and the electrolyte. This application achieves more significant improvement on performance of the soft-package lithium-ion battery, because the soft-package lithium-ion battery per se is prone to swelling during use, whereas this application could greatly reduce gas production of the battery and prevent from shortening the life of the battery due to the swelling of the soft-package lithium-ion battery.

In the lithium-ion battery of this application, in the compounds represented by the Formula I-1, the Formula I-2, and the Formula I-3:

The C₁-C₁₂ alkyl group may be a chain alkyl group or a cyclic alkyl group, and the chain alkyl group may be a linear alkyl group or a branched chain alkyl group. Hydrogen on a ring of the cyclic alkyl group may be further replaced by an alkyl group. A preferred lower limit of the quantity of carbon atoms in the C₁-C₁₂ alkyl group is 1, 2, 3, 4, or 5, and a preferred upper limit is 3, 4, 5, 6, 8, 10, or 12. Preferably, a C₁-C₁₀ alkyl group is selected. More preferably, a C₁-C₆ chain alkyl group or a C₃-C₈ cyclic alkyl group is selected. Furthermore preferably, a C₁-C₄ chain alkyl group or a C₅-C₇ cyclic alkyl group is selected. Examples of the C₁-C₁₂ alkyl group may specifically include a methyl group, an ethyl group, an n-propyl group, isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a hexyl group, a 2-methyl-pentyl group, a 3-methyl-pentyl group, a 1,1,2-trimethyl-propyl group, a 3,3-dimethyl-butyl group, a heptyl group, a 2-heptyl group, a 3-heptyl group, a 2-methylhexyl group, a 3-methylhexyl group, an isoheptyl group, an octyl group, a nonyl group, and a decyl group.

When the aforementioned C₁-C₁₂ alkyl group contains oxygen atoms, the C₁-C₁₂ alkyl group may be a C₁-C₁₂ alkoxy group. Preferably, a C₁-C₁₀ alkoxy group is selected. More preferably, a C₁-C₆ alkoxy group is selected. Furthermore preferably, a C₁-C₄ alkoxy group is selected. Examples of the C1-C12 alkoxy group may specifically include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, a sec-butoxy group, a t-butoxy group, an n-pentyloxy group, an isopentyloxy group, a cyclopentyloxy group, and a cyclohexyloxy group.

The C₂-C₁₂ alkenyl group may be a cyclic alkenyl group or a chain alkenyl group, and the chain alkenyl group may be a linear alkenyl group or a branched alkenyl group. In addition, preferably, the C₂-C₁₂ alkenyl group has one double bond. A preferred lower limit of the quantity of carbon atoms in the C₂-C₁₂ alkenyl group is 2, 3, 4, or 5, and a preferred upper limit is 3, 4, 5, 6, 8, 10, or 12. Preferably, a C₂-C₁₀ alkenyl group is selected. More preferably, a C₂-C₆ alkenyl group is selected. Furthermore preferably, a C₂-C₅ alkenyl group is selected. Examples of the C₂-C₁₂ alkenyl group may specifically include a vinyl group, an allyl group, an isopropenyl group, a pentenyl group, a cyclohexenyl group, a cycloheptenyl group, and a cyclooctenyl group.

The C₂-C₁₂ alkynyl group may be a cyclic alkynyl group or a chain alkynyl group, and the chain alkynyl group may be a linear alkynyl group or a branched alkynyl group. In addition, preferably, the C₂-C₁₂ alkynyl group has one triple bond. A preferred lower limit of the quantity of carbon atoms in the C₂-C₁₂ alkynyl group is 2, 3, 4, or 5, and a preferred upper limit is 3, 4, 5, 6, 8, 10, or 12. Preferably, a C₂-C₁₀ alkynyl group is selected. More preferably, a C₂-C₆ alkynyl group is selected. Furthermore preferably, a C₂-C₅ alkynyl group is selected. Examples of the C₂-C₁₂ alkynyl group may specifically include an ethynyl group, a propargyl group, an isopropynyl group, a pentynyl group, a cyclohexynyl group, a cycloheptynyl group, and a cyclooctynyl group.

The C₁-C₁₂ amine group may be selected from

where R′ and R″ are selected from the C₁-C₁₂ alkyl group.

The C₆-C₂₆ aryl group may be a phenyl group, a phenylalkyl group, a biphenyl group, or a fused ring aromatic hydrocarbon group (for example, a naphthyl group, an anthracenyl group, or a phenanthrenyl group). The biphenyl group and the fused ring aromatic hydrocarbon group may be further substituted with an alkyl group or an alkenyl group. Preferably, a C₆-C₁₆ aryl group is selected. More preferably, a C₆-C₁₄ aryl group is selected. Furthermore preferably, a C₆-C₉ aryl group is selected. Examples of the C₆-C₂₆ aryl group may specifically include a phenyl group, a benzyl group, a biphenyl group, a p-tolyl group, an o-tolyl group, an m-tolyl group, a naphthyl group, an anthracenyl group, and a phenanthryl group.

A hetero atom in the C₂-C₁₂ heterocyclic group may be selected from one or more of oxygen, nitrogen, sulfur, phosphorus, and boron, and a heterocyclic ring may be an aliphatic heterocyclic ring or an aromatic heterocyclic ring. Preferably, a C₂-C₁₀ heterocyclic group is selected. More preferably, a C₂-C₇ heterocyclic group is selected. Furthermore preferably, a five-membered aromatic heterocyclic ring, a six-membered aromatic heterocyclic ring, and a benzo heterocyclic ring are selected. Examples of the C₂-C₁₂ heterocyclic group may specifically include an ethylene oxide group, a propylene oxide group, an ethylene sulfide group, an aziridine group, a β-propiolactone group, a furyl group, a thienyl group, a pyrrolyl group, a thiazolyl group, an imidazolyl group, a pyridyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an indolyl group, and a quinolinyl group.

The halogen atom used as a substituent group may be selected from one or more of a fluorine atom, a chlorine atom, and a bromine atom. Preferably, the halogen atom is a fluorine atom.

(1) Specifically, the compound represented by the Formula I-1 is a polycyanopyrimidine compound.

In the Formula I-1:

Preferably, R₁, R₂, R₃, and R₄ each are independently selected from a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted C₁-C₆ linear or branched alkyl group, a substituted or unsubstituted C₅-C₉ cyclic alkyl group, a substituted or unsubstituted C₁-C₆ alkoxy group, a substituted or unsubstituted C₁-C₆ amine group, a substituted or unsubstituted C₂-C₆ alkenyl group, a substituted or unsubstituted C₂-C6 alkynyl group, a substituted or unsubstituted C₆-C₁₂ aryl group, or a substituted or unsubstituted C₂-C₁₂ heterocyclic group. More preferably, R₁, R₂, R₃, and R₄ each are independently selected from a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted C₁-C₃ linear or branched alkyl group, a substituted or unsubstituted C₅-C₇ cyclic alkyl group, a substituted or unsubstituted C₁-C₃ alkoxy group, a substituted or unsubstituted C₁-C₃ amine group, a substituted or unsubstituted C₂-C₃ alkenyl group, a substituted or unsubstituted C₂-C₃ alkynyl group, a substituted or unsubstituted C₆-C₈ aryl group, or a substituted or unsubstituted C₂-C₇ heterocyclic group. The substituent group is selected from one or more of halogen atoms.

Preferably, x is selected from integers 0-6; more preferably, is selected from integers 0-4; furthermore preferably, is selected from 0,1, or 2.

Preferably, y is selected from integers 0-6; more preferably, is selected from integers 0-4; furthermore preferably, is selected from 0,1, or 2.

Preferably, m is selected from 1 or 2.

Preferably, n is selected from 1 or 2.

Preferably, R₁ and R₃ are same groups. More preferably, R₁, R₃, and R₄ are all same groups.

Preferably, R₁ and R₃ are both hydrogen atoms. More preferably, R₁, R₃, and R₄ are all hydrogen atoms.

Preferably, R₁, R₂, R₃, and R₄ are all hydrogen atoms; or R₁, R₃, and R₄ are all hydrogen atoms, and R₂ is selected from a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted C₁-C₆ linear or branched alkyl group, or a substituted or unsubstituted C₁-C₆ alkoxy group. The substituent group is selected from one or more of halogen atoms. Preferably, the substituent group is selected from a fluorine atom.

Preferably, the compound represented by the Formula I-1 may be specifically selected from one or more of the following compounds, but this application is not limited thereto:

(2) Specifically, the compound represented by the Formula I-2 is a polynitrile piperazine compound.

In the Formula I-2:

Preferably, R₁, R₂, R₃, and R₄ each are independently selected from a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted C₁-C₆ linear or branched alkyl group, a substituted or unsubstituted C₅-C₉ cyclic alkyl group, a substituted or unsubstituted C₁-C₆ alkoxy group, a substituted or unsubstituted C₁-C₆ amine group, a substituted or unsubstituted C₂-C₆ alkenyl group, a substituted or unsubstituted C₂-C6 alkynyl group, a substituted or unsubstituted C₆-C₁₂ aryl group, or a substituted or unsubstituted C₂-C₁₂ heterocyclic group. More preferably, R₁, R₂, R₃, and R₄ each are independently selected from a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted C₁-C₃ linear or branched alkyl group, a substituted or unsubstituted C₅-C₇ cyclic alkyl group, a substituted or unsubstituted C₁-C₃ alkoxy group, a substituted or unsubstituted C₁-C₃ amine group, a substituted or unsubstituted C₂-C₃ alkenyl group, a substituted or unsubstituted C₂-C₃ alkynyl group, a substituted or unsubstituted C₆-C₈ aryl group, or a substituted or unsubstituted C₂-C₇ heterocyclic group. The substituent group is selected from one or more of halogen atoms.

Preferably, x is selected from integers 0-6; more preferably, is selected from integers 0-4; furthermore preferably, is selected from 0,1, or 2.

Preferably, y is selected from integers 0-6; more preferably, is selected from integers 0-4; furthermore preferably, is selected from 0,1, or 2.

Preferably, m is selected from 1 or 2.

Preferably, n is selected from 1 or 2.

Preferably, at least two of R₁, R₂, R₃, and R₄ are same groups. More preferably, at least three of R₁, R₂, R₃, and R₄ are same groups.

Preferably, at least two of R₁, R₂, R₃, and R₄ are hydrogen atoms. More preferably, at least three of R₁, R₂, R₃, and R₄ are hydrogen atoms.

Preferably, R₁, R₂, R₃, and R₄ are all hydrogen atoms; or three of R₁, R₂, R₃, and R₄ are hydrogen atoms, and the remaining one is selected from a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted C₁-C₆ linear or branched alkyl group, or a substituted or unsubstituted C₁-C₆ alkoxy group. The substituent group is selected from one or more of halogen atoms. Preferably, the substituent group is selected from a fluorine atom.

Preferably, the compound represented by the Formula I-2 may be specifically selected from one or more of the following compounds, but this application is not limited thereto:

(3) Specifically, the compound represented by the Formula I-3 is a polynitrile s-triazine compound.

In the Formula I-3:

Preferably, R₁, R₂, and R₃ each are independently selected from a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted C₁-C₆ linear or branched alkyl group, a substituted or unsubstituted C₅-C₉ cyclic alkyl group, a substituted or unsubstituted C₁-C₆ alkoxy group, a substituted or unsubstituted C₁-C₆ amine group, a substituted or unsubstituted C₂-C₆ alkenyl group, a substituted or unsubstituted C₂-C6 alkynyl group, a substituted or unsubstituted C₆-C₁₂ aryl group, or a substituted or unsubstituted C₂-C₁₂ heterocyclic group. More preferably, R₁, R₂, and R₃ each are independently selected from a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted C₁-C₃ linear or branched alkyl group, a substituted or unsubstituted C₅-C₇ cyclic alkyl group, a substituted or unsubstituted C₁-C₃ alkoxy group, a substituted or unsubstituted C₁-C₃ amine group, a substituted or unsubstituted C₂-C₃ alkenyl group, a substituted or unsubstituted C₂-C₃ alkynyl group, a substituted or unsubstituted C₆-C₈ aryl group, or a substituted or unsubstituted C₂-C₇ heterocyclic group. The substituent group is selected from one or more of halogen atoms.

Preferably, x is selected from integers 0-6; more preferably, is selected from integers 0-4; furthermore preferably, is selected from 0,1, or 2.

Preferably, y is selected from integers 0-6; more preferably, is selected from integers 0-4; furthermore preferably, is selected from 0,1, or 2.

Preferably, z is selected from integers 0-6; more preferably, is selected from integers 0-4; furthermore preferably, is selected from 0,1, or 2.

Preferably, m is selected from 1 or 2.

Preferably, n is selected from 1 or 2.

Preferably, k is selected from 1 or 2.

Preferably, at least two of R₁, R₂, and R₃ are same groups.

Preferably, at least two of R₁, R₂, and R₃ are hydrogen atoms.

Preferably, R₁, R₂, and R₃ are all hydrogen atoms; or two of R₁, R₂, and R₃ are hydrogen atoms, and the remaining one is selected from a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted C₁-C₆ linear or branched alkyl group, or a substituted or unsubstituted C₁-C₆ alkoxy group. The substituent group is selected from one or more of halogen atoms. Preferably, the substituent group is selected from a fluorine atom.

Preferably, the compound represented by the Formula I-3 may be specifically selected from one or more of the following compounds, but this application is not limited thereto:

In the lithium-ion battery of this application, the additive A may be synthesized by using the following method.

(1) Preparation of the Compound Represented by the Formula I-1

A reaction scheme is as follows:

A specific preparation process includes the following steps:

Adding aqueous solution P-2 with a concentration of 30%-40% dropwise to a raw material P-1 within 20 min-60 min, with quickly stirring the solution. After the dropwise addition is completed, quickly stirring the solution for 15 h-30 h. Stirring the solution in an oil bath at 70° C.-90° C. under reflux for 3 h-5 h to obtain a colorless, fuming, and viscous liquid intermediate product I-1-1. Then adding K₂CO₃, KI, and anhydrous acetonitrile, and quickly stirring them to form a solid-liquid mixture. Quickly adding a raw material P-3 at 40° C.-60° C., then stirring them for 10 h-20 h, and cooling the mixture to room temperature. Then performing separation and purification to obtain the compound represented by the Formula I-1.

(2) Preparation of the Compound Represented by the Formula I-2

A reaction scheme is as follows:

A specific preparation process includes the following steps:

Mixing anhydrous sodium carbonate, a raw material P-4, and a raw material P-3 in absolute ethanol, and stirring them for 2 h-5 h for a reaction. Repeatedly washing with hot ethanol for a plurality of times to obtain a crude product, and performing recrystallization to obtain the compound represented by the Formula I-2.

(3) Preparation of the Compound Represented by the Formula I-3

A reaction scheme is as follows:

A specific preparation process includes the following steps:

Mixing anhydrous sodium carbonate, a raw material P-5, and a raw material P-3 in absolute ethanol, and stirring them for 2 h-5 h for a reaction. Repeatedly washing with hot ethanol for a plurality of times to obtain a crude product, and performing recrystallization to obtain the compound represented by the Formula I-3.

In some embodiments, the lithium-ion battery may include an outer package for encapsulating the positive electrode plate, the electrode plate, and an electrolyte medium. In an example, the positive electrode plate, the negative electrode plate, and the separator may be laminated or wound to form an electrode assembly of a laminated structure or an electrode assembly of a wound structure, and the electrode assembly is encapsulated in an outer package. The electrolyte medium may be an electrolyte, which infiltrates in the electrode assembly. There may be one or more electrode assemblies in the lithium-ion battery, depending on needs.

In some embodiments, the outer package of the lithium-ion battery may be a soft package, for example, a soft bag. A material of the soft package may be plastic, for example, may include one or more of polypropylene PP, polybutylene terephthalate PBT, polybutylene succinate PBS, and the like. Alternatively, the outer package of the lithium-ion battery may be a hard shell, for example, an aluminum shell.

Shape of the lithium-ion battery in this application is not particularly limited, and may be of a cylindrical, square, or any other shape. FIG. 4 shows an example of a lithium-ion battery 5 of a square structure.

In some embodiments, lithium-ion batteries may be assembled into a battery module, and the battery module may include a plurality of lithium-ion batteries. A specific quantity may be adjusted based on application and capacity of the battery module.

FIG. 5 shows an example of a battery module 4. Referring to FIG. 5, in the battery module 4, a plurality of lithium-ion batteries 5 may be sequentially arranged along a length direction of the battery module 4; or certainly, may be arranged in any other manner. Further, the plurality of lithium-ion batteries 5 may be fixed by using fasteners.

Optionally, the battery module 4 may further include a housing with an accommodating space, and the plurality of lithium-ion batteries 5 are accommodated in the accommodating space.

In some embodiments, battery modules may be further assembled into a battery pack, and the quantity of battery modules included in the battery pack may be adjusted based on application and capacity of the battery pack.

FIG. 6 and FIG. 7 show an example of a battery pack 1. Referring to FIG. 6 and FIG. 7, the battery pack 1 may include a battery cabinet and a plurality of battery modules 4 disposed in the battery cabinet. The battery cabinet includes an upper cabinet body 2 and a lower cabinet body 3. The upper cabinet body 2 can cover the cabinet body 3 and form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery cabinet in any manner.

An apparatus according to a second aspect of this application is described next.

A second aspect of this application provides an apparatus. The apparatus includes the lithium-ion battery in the first aspect of this application, and the lithium-ion battery supplies power to the apparatus. The apparatus may be, but not limited to, a mobile device (for example, a mobile phone or a notebook computer), an electric vehicle (for example, a full electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf vehicle, or an electric truck), an electric train, a ship, a satellite, an energy storage system, and the like.

A lithium-ion battery, a battery module, or a battery pack may be selected for the apparatus according to requirements for using the apparatus.

FIG. 8 shows an example of an apparatus. The apparatus is a full electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like. To meet a requirement of the apparatus for high power and a high energy density of a lithium-ion battery, a battery pack or a battery module may be used.

In another example, the apparatus may be a mobile phone, a tablet computer, a notebook computer, or the like. The apparatus is generally required to be light and thin, and may use a lithium-ion battery as its power source.

To make the objectives, technical solutions, and beneficial technical effects of this application clearer, this application is further described below in detail with reference to embodiments. It should be understood that the embodiments described in this specification are merely intended to explain this application, but not to limit this application. Formulations, proportions, and the like of the embodiments may be adjusted according to local conditions without substantial effect on results.

All reagents, materials, and instruments that are used in Examples and Comparative Examples are commercially available unless otherwise specified. Specific synthesis processes of additives A1, A2, and A3 are as follows. Other types of additives A may be synthesized according to similar methods.

Synthesis of the Additive A1:

37% formaldehyde aqueous solution was added dropwise to 1,3-propanediamine within 0.5 h with quick stirring. After the completion of dropwise addition, the solution was still quickly stirred for 20 h. Then the solution was stirred in an oil bath at 80° C. reflux for 4 h to obtain intermediate product hexahydropyrimidine as a colorless, fuming, and viscous liquid. K₂CO₃, KI, and anhydrous acetonitrile were added, followed by quick stirring to form a solid-liquid mixture. Then β-chloropropionitrile was added at 60° C. within 0.5 h. The mixture was stirred for 17 h, and cooled to room temperature. Then the mixture was subjected to separation and purification to obtain A1. Carbon nuclear magnetic resonance spectroscopy was shown in FIG. 1.

Synthesis of the Additive A2:

Anhydrous sodium carbonate, piperazine, and β-chloropropionitrile were mixed in absolute ethanol, and stirred for 4 h for reaction. The mixture was repeatedly washed with hot ethanol for a plurality of times to obtain a crude product, and subjected to recrystallization to obtain A2. Carbon nuclear magnetic resonance spectroscopy was shown in FIG. 2.

Synthesis of the Additive A3:

Anhydrous sodium carbonate, 1,3,5-s-triazine, and chloroacetonitrile were mixed in absolute ethanol, and stirred for 4 h for reaction. The mixture was repeatedly washed with hot ethanol for a plurality of times to obtain a crude product, and subjected to recrystallization to obtain A3. Carbon nuclear magnetic resonance spectroscopy was shown in FIG. 3.

In Examples 1-30 and reference Comparative Examples 1-2, lithium-ion batteries was prepared according to the following method.

(1) Preparation of an Electrolyte

A mixed solution of ethylene carbonate (EC for short), ethyl methyl carbonate (EMC for short) and diethyl carbonate (DEC for short) was used as an organic solvent, where a mass ratio of EC, EMC, and DEC was 1:1:1. LiPF₆ was used as a lithium salt in an amount of 12.5% relative to the total mass of the electrolyte. Additives were added according to electrolyte composition as shown in Table 1, where percents of all additive components are calculated relative to the total mass of the electrolyte.

Additives A used in the Examples and Comparative Examples were abbreviated as follows:

(2) Preparation of a Positive Electrode Plate

A positive active material, a binder PVDF, and a conductive agent acetylene black in Table 1 based on a mass ratio of 98:1:1 were mixed. N-methylpyrrolidone was added. The resulting mixture was stirred by using a vacuum mixer until the mixture was stable and uniform, to obtain a positive slurry. The positive slurry was uniformly applied onto an aluminum foil. The aluminum foil was dried at room temperature, and transferred to a blast oven at 120° C. for 1 h. Then the aluminum foil was cold-pressed and cut to obtain a positive electrode plate.

(3) Preparation of a Negative Electrode Plate

A negative active material graphite, a conductive agent acetylene black, a thickening agent sodium carboxymethyl cellulose, and a binder styrene-butadiene rubber based on a mass ratio of 97:1:1:1 were mixed. Deionized water was added. The resulting mixture was stirred by using a vacuum mixer until the mixture was stable and uniform, to obtain a negative slurry. The negative slurry was uniformly applied onto a copper foil. The copper foil was dried at room temperature, and transferred to a blast oven at 120° C. for 1 h. Then the copper foil was cold-pressed and cut to obtain a negative electrode plate.

(4) Preparation of a Lithium-Ion Battery

The positive electrode plate, the negative electrode plate, and a PP/PE/PP separator were wound to obtain an electrode assembly. The electrode assembly was placed into an aluminum-plastic film of a packaging bag, followed by injection of the electrolyte. Then a procedure including sealing, standing, hot-pressing and cold-pressing, forming, gas exhausting, and capacity testing were performed to obtain a lithium-ion battery.

TABLE 1 Parameters of Examples 1-30 and Comparative Examples 1-2 Additive A Additive B Additive C Positive active material Type Amount Type Amount Type Amount Example 1 Li_(1.05)Co_(0.98)Mg_(0.005)Zr_(0.005)Ti_(0.01)O_(1.9)F_(0.1) A1 0.1% / / / / Example 2 Li_(1.05)Co_(0.98)Mg_(0.005)Zr_(0.005)Ti_(0.01)O_(1.9)F_(0.1) A1 1.0% / / / / Example 3 Li_(1.05)Co_(0.98)Mg_(0.005)Zr_(0.005)Ti_(0.01)O_(1.9)F_(0.1) A1 2.0% / / / / Example 4 Li_(1.05)Co_(0.98)Mg_(0.005)Zr_(0.005)Ti_(0.01)O_(1.9)F_(0.1) A1 3.5% / / / / Example 5 Li_(1.05)Co_(0.98)Mg_(0.005)Zr_(0.005)Ti_(0.01)O_(1.9)F_(0.1) A1 6.0% / / / / Example 6 Li_(1.05)Co_(0.98)Mg_(0.005)Zr_(0.005)Ti_(0.01)O_(1.9)F_(0.1) A1 8.0% / / / / Example 7 Li_(1.05)Co_(0.98)Mg_(0.005)Zr_(0.005)Ti_(0.01)O_(1.9)F_(0.1) A1 10.0% / / / / Example 8 Li_(1.01)Co_(0.98)Mg_(0.01)Ti_(0.005)Al_(0.005)O₂ A2 2.0% / / / / Example 9 Li_(1.1)Co_(0.95)Mg_(0.01)Zr_(0.01)Al_(0.03)O₂ A3 2.0% / / / / Example 10 Li_(1.04)Co_(0.95)Mg_(0.02)Zr_(0.03)O_(1.95)F_(0.05) A4 2.0% / / / / Example 11 Li_(1.08)Co_(0.97)Mg_(0.01)Zr_(0.01)Al_(0.01)O_(1.9)S_(0.1) A5 2.0% / / / / Example 12 Li_(1.085)Co_(0.98)Zr_(0.01)Ti_(0.005)Al_(0.005)O_(1.9)Cl_(0.1) A6 2.0% / / / / Example 13 Li_(1.03)Co_(0.96)Mg_(0.01)Zr_(0.01)Ti_(0.01)Al_(0.01)O₂ A7 2.0% / / / / Example 14 Li_(1.06)Co_(0.96)Mg_(0.02)Ti_(0.02)O₂ A8 2.0% / / / / Example 15 Li_(1.09)Co_(0.98)Mg_(0.01)Ti_(0.005)Al_(0.005)O₂ A9 2.0% / / / / Example 16 Li_(1.04)Co_(0.97)Zr_(0.01)Al_(0.02)O_(1.9)F_(0.1) A10  2.0% / / / / Example 17 Li_(1.07)Co_(0.97)Zr_(0.01)Ti_(0.01)Al_(0.01)O_(1.9)S_(0.1) A11  2.0% / / / / Example 18 Li_(1.02)Co_(0.96)Mg_(0.02)Zr_(0.015)Ti_(0.005)O_(1.9)S_(0.1) A12  2.0% / / / / Example 19 Li_(1.03)Co_(0.98)Ti_(0.01)Al_(0.01)O_(1.9)Cl_(0.1) A13  2.0% / / / / Example 20 Li_(1.05)Co_(0.97)Mg_(0.01)Zr_(0.01)Al_(0.01)O_(1.9)Cl_(0.1) A14  2.0% / / / / Example 21 Li_(1.04)Co_(0.95)Zr_(0.02)Ti_(0.03)O_(1.9)F_(0.1) A15  2.0% / / / / Example 22 Li_(1.09)Co_(0.97)Mg_(0.02)Ti_(0.01)O_(1.95)F_(0.05) A16  2.0% / / / / Example 23 Li_(1.03)Co_(0.95)Mg_(0.03)Ti_(0.02)O_(1.9)S_(0.1) A17  2.0% / / / / Example 24 Li_(1.04)Co_(0.97)Zr_(0.01)Ti_(0.01)Al_(0.01)O_(1.9)S_(0.1) A18  2.0% / / / / Example 25 Li_(1.05)Co_(0.98)Mg_(0.005)Zr_(0.005)Ti_(0.01)O_(1.9)F_(0.1) A1 2.0% LiBF₄ 2.0% / / Example 26 Li_(1.05)Co_(0.98)Mg_(0.005)Zr_(0.005)Ti_(0.01)O_(1.9)F_(0.1) A2 2.0% LiBF₄ 2.0% / / Example 27 Li_(1.05)Co_(0.98)Mg_(0.005)Zr_(0.005)Ti_(0.01)O_(1.9)F_(0.1) A3 2.0% LiBF₄ 2.0% / / Example 28 Li_(1.05)Co_(0.98)Mg_(0.005)Zr_(0.005)Ti_(0.01)O_(1.9)F_(0.1) A1 2.0% / / VC 2.0% Example 29 Li_(1.05)Co_(0.98)Mg_(0.005)Zr_(0.005)Ti_(0.01)O_(1.9)F_(0.1) A2 2.0% / / FEC 2.0% Example 30 Li_(1.05)Co_(0.98)Mg_(0.005)Zr_(0.005)Ti_(0.01)O_(1.9)F_(0.1) A3 2.0% / / PS 2.0% Comparative LiCoO₂ / / / / / / Example 1 Comparative Li_(1.05)Co_(0.98)Mg_(0.005)Zr_(0.005)Ti_(0.01)O_(1.9)F_(0.1) Adiponitrile 2.0% / / / / Example 2

Tests for lithium-ion battery are described below.

(1) Cycle Performance Test For a Lithium-Ion Battery at Normal Temperature and High Voltage

At 25° C., the lithium-ion battery is charged at a constant current of 1 C until a voltage of 4.35 V is reached, further charged at a constant voltage of 4.35 V until a current of 0.05 C is reached, and then discharged at a constant current of 1 C until a voltage of 3.0 V is reached. This is a charge/discharge cycle process, and the obtained discharge capacity at this time is the discharge capacity at the first cycle. A lithium-ion battery is subjected to charge/discharge test according to the foregoing method for 200 cycles, to determine a discharge capacity at the 200^(th) cycle.

Capacity retention rate (%) of the lithium-ion battery after 200 cycles=(the discharge capacity of the lithium-ion battery after 200 cycles/the discharge capacity of the lithium-ion battery at the first cycle)×100%.

(2) Cycle Performance Test For a Lithium-Ion Battery Under High-Temperature and High-Voltage Conditions

At 45° C., the lithium-ion battery is charged at a constant current of 1 C until a voltage of 4.35 V is reached, further charged at a constant voltage of 4.35 V until a current of 0.05 C is reached, and then discharged at a constant current of 1 C until a voltage of 3.0 V is reached. This is a charge/discharge cycle process, and the obtained discharge capacity at this time is the discharge capacity at the first cycle. A lithium-ion battery is subjected to charge/discharge test according to the foregoing method for 200 cycles, to determine a discharge capacity at the 200^(th) cycle.

Capacity retention rate (%) of a lithium-ion battery after 200 cycles=(the discharge capacity of the lithium-ion battery after 200 cycles/the discharge capacity of the lithium-ion battery at the first cycle)×100%.

(3) Storage Performance Test For a Lithium-Ion Battery at High Temperature

At 25° C., the lithium-ion battery is charged at a constant current of 0.5 C until a voltage of 4.35 V is reached, and then charged at a constant voltage of 4.35 V until a current of 0.05 C is reached. The thickness of the lithium-ion battery is tested and denoted the thickness as h₀. Then the lithium-ion battery is placed in a constant-temperature box at 85° C., stored for 24 h, and then taken out. Then the thickness of the lithium-ion battery is tested again and denoted as h₁.

Thickness expansion rate (%) of the lithium-ion battery after storage at 85° C. for 24 h=[(h₁−h₀)/h₀]×100%.

The lithium-ion batteries were tested in the above tests.

TABLE 2 Performance test results of Examples 1-30 and Comparative Examples 1-2 Capacity retention Capacity retention Thickness rate after 200 cycles rate after 200 cycles expansion rate at 25° C./4.35 V at 45° C./4.35 V at 85° C./24 h Example 1 89% 82% 25% Example 2 96% 92% 10% Example 3 98% 94%  5% Example 4 96% 91%  4% Example 5 93% 86%  2% Example 6 88% 79%  2% Example 7 83% 72%  1% Example 8 97% 93%  4% Example 9 96% 92%  6% Example 10 98% 94%  8% Example 11 95% 91%  4% Example 12 95% 91%  5% Example 13 97% 93%  5% Example 14 95% 91%  6% Example 15 96% 92%  7% Example 16 96% 92%  4% Example 17 96% 92%  8% Example 18 98% 94%  9% Example 19 97% 93%  6% Example 20 96% 92%  7% Example 21 94% 90%  5% Example 22 98% 94%  3% Example 23 96% 92%  6% Example 24 97% 93%  4% Example 25 99% 96%  2% Example 26 98% 96%  3% Example 27 98% 95%  3% Example 28 97% 94%  6% Example 29 99% 96%  5% Example 30 96% 94%  4% Comparative 85% 78% 42% Example 1 Comparative 89% 81% 14% Example 2

It can be seen from comparisons between Examples 1-30 and Comparative Examples 1-2 that the lithium-ion batteries of this application have super cycle performance and storage performance under high-temperature and high-voltage conditions.

Compared with Comparative Example 1, in Examples of this application, the metal ion M-doped lithium cobalt oxide material Li_(x1)Co_(y1)M_(1-y1)O_(2-z1)Q_(z1) was used as the positive active material, and the additive A was used as an electrolyte additive. The doping element M served as a framework in the positive active material. This reduced lattice deformation of the positive active material during deep delithiation, delayed degradation of bulk structure of the positive active material, and greatly improved structural stability of the lithium-ion battery when the lithium-ion battery was used at high voltage. The additive A was a polynitrile six-membered nitrogen-heterocyclic compound with a relatively low oxidation potential, such that a stable complex layer was formed on a surface of the positive active material during formation of the battery. This effectively passivated the surface of the positive active material, reduced surface activity of the positive active material, and avoided direct contact between the electrolyte and the surface of the positive active material, thereby greatly reducing surface side reactions, and correspondingly reducing lithium ions consumed in the side reactions, and thus greatly decreasing a consumption rate of reversible lithium ions. The actual effect finally manifested was that capacity retention rate of the lithium-ion battery after cycling was greatly increased. Due to the production gas in some surface side reactions, the reduction of surface side reactions further indicated a decrease in gas production of the battery. The actual effect finally manifested was that thickness expansion of the lithium-ion battery was significantly reduced at high temperature.

Compared with the linear nitrile compound used in Comparative Example 2, the polynitrile six-membered nitrogen-heterocyclic compound in Examples had a special six-membered nitrogen-heterocyclic structure with a spacing between nitrile groups closer to that between transition metals on the surface of the positive active material. This could maximize complexation of the nitrile groups and allow more nitrile groups to have a complexation effect. Therefore, the polynitrile six-membered nitrogen-heterocyclic compound in Examples had stronger coverage on a transition metal on the surface of the positive active material, better passivation on the surface of the positive active material, and also outstanding improvement on cycle performance and storage performance of the lithium-ion battery.

It can be further seen from Examples 1-7 that, when an end-of-charge voltage was fixed at 4.35 V, with an increase (from 0.1% to 10%) in the amount of the additive A, the capacity retention rate of the lithium-ion battery after cycling at 25° C. and 45° C. showed an ascent and then showed a decline trend, and the thickness expansion rate after storage at 85° C. for 24 h was decreasing. This was because when the amount of the additive A was relatively large, the complex layer formed by the additive A being adsorbed on the surface of the positive active material was likely to be thicker and denser, affecting diffusion and migration of lithium ions, and greatly increasing positive electrode impedance. Secondly, the additive A consumed lithium ions while forming the complex layer, reducing lithium ions available for cycling. Finally, a relatively large amount of the additive A caused an increase in overall viscosity of the electrolyte and a decrease in an ionic conductivity, so that the capacity retention rate of the lithium-ion battery after cycling at 25° C. and 45° C. showed an ascent and then showed a decline trend. Therefore, the amount of the additive A needs to be appropriate. Preferably, the amount is 0.1%-10%; more preferably, is 0.1%-6%; furthermore preferably, is 0.1%-3.5%.

Examples 25-27 studied the effect of LiBF₄ on the performance of the lithium-ion battery when the amount of the additive A was relatively preferred. Compared with Example 3, in Examples 25-28, the thickness expansion rates after storage at 85° C. for 24 h were lower. This was because atoms B in LiBF₄ stabilized oxygen atoms in the positive active material and had an effect of suppressing oxygen release of the positive active material. As a result, the lithium-ion battery showed better storage performance.

Examples 28-30 studied the effect of VC, FEC, and PS on the performance of the lithium-ion battery when the amount of the additive A was relatively preferred. These additives helped form, on surfaces of positive and negative electrodes, a surface film containing double bonds, fluorine atoms, or sulfonate groups. The surface film had good chemical, electrochemical, mechanical, and thermal stability, and could avoid direct contact between the electrolyte and the surfaces of the positive and negative electrodes while smoothly conducting lithium ions, thereby providing an effect of suppressing oxidation and reduction side reaction on the surfaces of the positive and negative electrodes. Therefore, adding the additives helps further improve the cycle performance and the storage performance of the lithium-ion battery.

According to the disclosure and guidance in this specification, a person skilled in the art to which this application relates may also make appropriate changes and modifications to the foregoing embodiments. Therefore, this application is not limited to the specific embodiments disclosed and described above, and modifications and changes to this application shall also fall within the protection scope of the claims of this application. In addition, although some specific terms are used in this specification, these terms are merely intended for ease of description, and do not constitute any limitation on this application. 

What is claimed is:
 1. A lithium-ion battery, comprising an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive electrode plate, a negative electrode plate, and a separator, wherein a positive active material of the positive electrode plate comprises Li_(x1)Co_(y1)M_(1-y1)O_(2-z1)Q_(z1), where 0.5≤x1≤1.2, 0.8≤y1≤1.0, 0≤z1≤0.1, M is selected from one or more of Al, Ti, Zr, Y, and Mg, and Q is selected from one or more of F, Cl, and S; the electrolyte contains an additive A represented by Formula I-2; and

in the Formula I-2, R₁, R₂, R₃, and R₄ each are independently selected from a hydrogen atom, a halogen atom, a substituted or unsubstituted C1-C3 linear or branched alkyl group, a substituted or unsubstituted C5-C7 cyclic alkyl group, a substituted or unsubstituted C1-C3 alkoxy group, a substituted or unsubstituted C1-C3 amine group, a substituted or unsubstituted C2-C3 alkenyl group, a substituted or unsubstituted C2-C3 alkynyl group, a substituted or unsubstituted C6-C8 aryl group, or a substituted or unsubstituted C2-C7 heterocyclic group, wherein a substituent group is selected from one or more of halogen atoms; x and y each are independently selected from 0, 1, or 2; and m and n each are independently selected from 1 or
 2. 2. The lithium-ion battery according to claim 1, wherein at least two of R₁, R₂, R₃, and R₄ are same groups, preferably, at least three of R₁, R₂, R₃, and R₄ are same groups.
 3. The lithium-ion battery according to claim 2, wherein at least two of R₁, R₂, R₃, and R₄ are hydrogen atoms, preferably, at least three of R₁, R₂, R₃, and R₄ are hydrogen atoms.
 4. The lithium-ion battery according to claim 1, wherein the additive A is selected from one or more of the following compounds:


5. The lithium-ion battery according to claim 1, wherein based on total mass of the electrolyte, mass percent of the additive A is 0.1%-10%, preferably 0.1%-6%, more preferably 0.1%-3.5%.
 6. The lithium-ion battery according to claim 1, wherein the electrolyte further contains an additive B that is LiBF₄, and based on total mass of the electrolyte, mass percent of the additive B is 0.1%-10%, preferably 0.1%-5%.
 7. The lithium-ion battery according to claim 1, wherein the electrolyte further contains an additive C that is selected from one or more of vinylene carbonate, fluoroethylene carbonate, and 1,3-propane sultone, and based on the total mass of the electrolyte, mass percent of the additive C is 0.1%-10%, preferably 0.1%-5%.
 8. The lithium-ion battery according to claim 6, wherein the electrolyte further contains an additive C that is selected from one or more of vinylene carbonate, fluoroethylene carbonate, and 1,3-propane sultone, and based on the total mass of the electrolyte, mass percent of the additive C is 0.1%-10%, preferably 0.1%-5%.
 9. The lithium-ion battery according to claim 1, wherein the lithium-ion battery is a hard-shell lithium-ion battery or a soft-package lithium-ion battery.
 10. The lithium-ion battery according to claim 1, wherein an end-of-charge voltage of the lithium-ion battery is not less than 4.2 V, preferably not less than 4.35 V.
 11. An apparatus, comprising the lithium-ion battery according to claim
 1. 